In the past, there has been proposed an LED lighting device including a driving circuit for a cooling device for cooling an LED used as a light source. For example, such an LED lighting device is disclosed in document 1 (JP 2011-150936 A).
The LED lighting device disclosed in this document 1 includes a DC power source, a series circuit connected to a plurality of LEDs, and a cooling device driver for dissipating heat generated by the LEDs. The cooling device driver is connected in parallel with at least one LED of the series circuit. Thus, a DC voltage developed across the LED of the series circuit is supplied to the cooling device driver.
Additionally, the cooling device driver is connected to a temperature detecting device which is, for example, a temperature detector such as a thermistor. This temperature detecting device measures a temperature of the LED, and provides a detection signal relating to the LED to the cooling device driver. The cooling device driver operates a fan motor according to the detection signal.
The aforementioned prior art uses one temperature detecting device. When a high power LED is employed as the light source, the light source tends to be large in size and therefore it is difficult to measure a temperature of the entire light source by use of one temperature detecting device. In this case, even if the light source is cooled based on the temperature measured, temperatures of some regions of the light source are different, and accordingly a light output thereof is likely to be unstable. Also, in this case, the LED is likely to have such a local temperature that exceeds an allowable operating temperature, and this would cause a great deterioration in luminous flux and a great decrease in lifetime, and in some cases, the light source is turned off.